1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a facsimile machine, and a printer.
2. Description of the Related Art
An electrophotographic image forming apparatus generally includes a cleaning device that cleans a surface of an image carrier by removing residual toner remained on the surface of the image carrier after an image transfer process so that the surface of the image carrier can repeatedly be used for image formation. A cleaning device having a cleaning blade formed of an elastic member made of polyurethane rubber and the like is generally used as the above cleaning device because it has a simple structure and good toner removal capability. Furthermore, an image forming apparatus that includes a lubricant supply device has been proposed, in which the lubricant supply device supplies lubricant made of fatty acid metal salt and the like to the surface of the image carrier in order to reduce a coefficient of friction between the above-mentioned cleaning blade and the surface of the image carrier. In such an image forming apparatus, when the amount of the lubricant supplied to the surface of the image carrier is too small, the coefficient of friction cannot sufficiently be reduced, so that failures due to a high coefficient of friction (e.g., cleaning blade burr or shortening of the lifetime of the image carrier) cannot fully be prevented. On the other hand, when the amount of the lubricant supplied to the surface of the image carrier is too large, an amount of the lubricant that gets attached to various members and devices placed around the image carrier increases, so that failures due to the attached lubricant (e.g., occurrence of abnormal images due to the lubricant attached to a charging member and a developer holding member) markedly increase. Therefore, in the image forming apparatus that includes a mechanism for supplying lubricant to the surface of the image carrier, it is important to perform control to optimize the amount of the lubricant to be supplied to the surface of the image carrier.
Some of such image forming apparatuses as described above are configured to supply lubricant to the surface of the image carrier at a position upstream of a contact portion of the cleaning blade and the surface of the image carrier in a surface movement direction of the image carrier. In this configuration, the cleaning blade also functions to spread and level out the lubricant supplied to the surface of the image carrier. Therefore, it is possible to level out the lubricant supplied to the surface of the image carrier to some extent without providing a lubricant leveling member for leveling out the lubricant in addition to the cleaning blade. However, in this configuration, because the lubricant slips into the contact portion of the cleaning blade together with residual toner, the amount of the lubricant may vary between an area where the residual toner is present and an area where the residual toner is not present. Therefore, the lubricant cannot fully be leveled out. In this case, the amount of the lubricant may be too large or too small in some portions on the surface of the image carrier, so that the above-mentioned failures may occur locally. Furthermore, in the above-mentioned configuration, some lubricant is attached to the residual toner and removed together with the toner. In this case, it is difficult to accurately recognize the amount of the lubricant to be removed, so that it is difficult to control the supply amount and the consumption amount of the lubricant. As a result, the above-mentioned failures are likely to occur.
On the other hand, Japanese Patent Application Laid-open No. 2000-330443 discloses an image forming apparatus that includes a lubricant supply means arranged downstream of a contact portion of a cleaning blade and an image carrier in a surface movement direction of the image carrier, and also includes a lubricant leveling blade arranged downstream of the lubricant supply means and used for leveling out the lubricant. In this image forming apparatus, because the surface of the image carrier is already cleaned when the lubricant is to be supplied thereto, the lubricant supplied to the surface of the image carrier can fully be leveled out by the lubricant leveling blade. Furthermore, it is possible to prevent the lubricant from getting attached to toner and removed together with the toner. Therefore, it is possible to easily control the supply amount and the consumption amount of the lubricant. The lubricant leveling blade disclosed in Japanese Patent Application Laid-open No. 2000-330443 is arranged such that a ridge portion of the lubricant leveling blade comes into contact with the surface of the image carrier so that the ridge portion intersects with the surface movement direction of the surface of the image carrier in order to level out the lubricant supplied to the surface of the image carrier. Thus, this lubricant leveling blade is a right-angle blade in which a blade corner portion angle formed by two planes, one of which faces the surface of the image carrier on the upstream side and the other of which faces the surface of the image carrier on the downstream side in the surface movement direction of the surface of the image carrier across the ridge portion being in contact with the surface of the image carrier, is set to a right angle.
In recent years, a demand for long-term maintenance free operations of image forming apparatuses has been growing, and it has been desired to maintain functions of the lubricant leveling blade at a constant level over a long period of time from the initial time. To maintain the functions of the lubricant leveling blade, it is necessary to reduce the amount of abrasion that occurs on the ridge portion of the lubricant leveling blade being in contact with the surface of the image carrier over time.
Japanese Patent Application Laid-open No. 2008-276125 discloses a technology for reducing the amount of abrasion that occurs on the ridge portion being in contact with the surface of the image carrier over time by using, as the lubricant leveling blade, an obtuse-angle blade in which the blade corner portion angle formed by two planes, one of which faces the surface of the image carrier on the upstream side and the other of which faces the surface of the image carrier on the downstream side in the surface movement direction of the surface of the image carrier across the ridge portion being in contact with the surface of the image carrier, is set to an obtuse angle.
However, although the amount of abrasion that occurs on the ridge portion being in contact with the surface of the image carrier over time can be reduced by using the obtuse-angle blade as the lubricant leveling blade, the process cost of the obtuse-angle blade is higher than that of the right-angle blade. Therefore, if the obtuse-angle blade is used as a lubricant leveling blade in each image forming device of an image forming apparatus that includes a plurality of image forming devices like a full-color image forming apparatus that uses four colors, manufacturing costs increase because of increase in the process cost of the lubricant leveling blades by the number of the image forming devices. In view of this, it is desirable to decrease the number of image forming devices that use the obtuse-angle blades as the lubricant leveling blades as much as possible.
Incidentally, a blade member, which can reduce the amount of abrasion that occurs on the ridge portion being in contact with the surface of the image carrier over time when it is configured as the obtuse-angle blade, may be applied to not only the lubricant leveling blade but also any blade members.